1. Field of the Invention
The present general inventive concept relates to a developing cartridge and an image forming apparatus having the developing cartridge, and more particularly, to a developing cartridge which includes a charging unit using a tubular member and an image forming apparatus which has the developing cartridge.
2. Description of the Related Art
An image forming apparatus such as a printer, facsimile, copier, multifunction peripheral (MFP) and the like forms a prescribed image in a print medium using electrophotography. In general, such an image forming apparatus consists of charging, exposure, development, transfer of a developed image, and fixing processes so as to form an image on a print medium. In the charging process, a charging unit charges a photoconductive body to a prescribed electric potential. In the exposure process, a laser scanning unit scans the photoconductive body charged to the prescribed electric potential with a laser so as to form an electrostatic latent image corresponding to printing data on the photoconductive body. In the development process, a developing unit develops a toner image by supplying toner to the photoconductive body on which the electrostatic latent image is formed. In the transfer process, a transfer unit transfers the toner image formed on the photoconductive body to the printing data. In the fixing process, a fixing unit fixes the toner transferred to the printing data, thereby forming a prescribed image in the print medium. Thereafter, the print medium is discharged outside the image forming apparatus and the printing is completed.
A charging unit may be generally divided by using a non-contact charging system or contact charging system. A charging unit according to the non-contact charging system uses corona discharge typically. The charging unit using the corona discharge has the advantage of charging a photoconductive body uniformly, but leads to producing discharge products such as ozone. Therefore, a separate unit is required to dispose of the discharge products such as ozone, etc., and this addition of a separate unit results in increasing a size of the image forming apparatus and costs for manufacturing the same.
A charging unit using the contact charging system may be divided by using a conductive roller, a conductive brush, a film-shaped charging electrode or a tube-shaped structure, etc.
A charging unit employing the conductive roller needs a support device for the roller and the like, and has a complex construction. An elastic roller must be in close contact with a charge acceptor so that a stable minute gap is formed to charge the charge acceptor uniformly, and hence, the hardness of rubber must be comparatively low. Such rubber contains a comparatively large amount of process oil. Such a charging unit has a problem of affecting image quality adversely due to contamination of a surface of the charge acceptor, caused by the process oil. Further, a rubber roller should be in a higher dimensional accuracy, and this leads to increasing the manufacturing costs.
A charging unit employing the conductive brush is advantageous in uniform contact, as compared with the elastic roller. However, the conductive brush is manufactured at a high manufacturing cost and is likely to form brush marks that cause irregular charging adversely affecting the image.
A charging unit employing the film-shaped charging electrode vibrates due to frictional electrification because a working edge of the film-shaped charging electrode is in contact with the charge acceptor, whereby the charging potential is liable to be caused to become unstable. Furthermore, if foreign matters, such as toner and additives, adhere to the working edge of the film-like charging electrode, creeping discharge occurs to cause defective stripes of charges. A method to solve such a problem applies both a DC voltage and an AC voltage simultaneously to the film-shaped charging electrode. However, the AC voltage generates vibrations resonant with the frequency of the AC voltage and generates charging noise.
A charging unit employing the cylindrical (tube-shaped) structure has problems such as a slip phenomenon of a tubular member occurring due to a frictional force produced between the tubular member and an elastic member, and also a bias occurring due to an axial force resulting from the pressure difference between left and right when being driven for rotation.